Introduction: Dysmenorrehea is one of the most common side effects of IUD. Considering public enthusiasm to the use of herbal medicine and positive effects of cumin on muscle cramps, this study conducted to compare the effects of cumin and mefenamic acid capsules on secondary dysmenorrhea due to IUD.

Methods: This crossover triple-blind randomized clnical trial study was performed on 100 IUD users who came to 6 health centers in Karaj.Research took place in three stages.In the first stage severity of dysmenorrehea was measured using Visual Analogue Scale (VAS).In the second stage all participants were randomly allocated to mefenamic acid and cumin groups. They took capsules for two consecutive cycle. In the third stage each research unit received the same treatment of the opposite group with replacing the medicine for two more consecutive cycle.Severity of pain was assessed using VAS for 5 cycle. Considering that the maximum efficacy time for cumin was 24 hours and for Mefenamic acid was 6 to 8 hours,the use of drugs in 7 days duringmenstruation,had no effect on subsequent cycles. Data, was analyse by Chi-square and Fisher's exact test, paired t-test, Wilcoxon,and one way ANOVA.

Results :The mean pain intensity before treatment was 4.28 ± 1.72 and after treatment was 1.89 ± 1.37 and 2.01 ± 1.33 in the mefenamic acid and cumin groups. There was a significant difference in decrease of pain intensity in both groups(P<0.001).There wasn’t a significant difference in decrease of pain intensity between two groups.

Conclusion : This study showed that cumin same as mefenamic acid capsules can decrease the severity of dysmenorrehea effectively.Therefore it is recommended to use it in the treatment of secondary dysmenorrhea due to IUD.